A number of publications are cited herein in order to more fully describe and disclose the invention and the state of the art to which the invention pertains. Each of these references is incorporated herein by reference in its entirety into the present disclosure, to the same extent as if each individual reference was specifically and individually indicated to be incorporated by reference.
Throughout this specification, including the claims which follow, unless the context requires otherwise, the word “comprise,” and variations such as “comprises” and “comprising,” will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps.
It must be noted that, as used in the specification and the appended claims, the singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to “a pharmaceutical carrier” includes mixtures of two or more such carriers, and the like.
Ranges are often expressed herein as from “about” one particular value, and/or to “about” another particular value. When such a range is expressed, another embodiment includes from the one particular value and/or to the other particular value. Similarly, when values are expressed as approximations, by the use of the antecedent “about,” it will be understood that the particular value forms another embodiment.
This disclosure includes information that may be useful in understanding the present invention. It is not an admission that any of the information provided herein is prior art or relevant to the presently claimed invention, or that any publication specifically or implicitly referenced is prior art.
Cyclin-Dependent Protein Kinase (CDK)
Cyclin-dependent protein kinases (CDK) are the catalytic subunits of a family of 21 serine/threonine protein kinases (see, e.g., Malumbres et al., 2009), some of which control progression of the cell through the stages of growth, DNA replication and mitosis (see, e.g., Pines, 1995; Morgan, 1995). Activation of specific CDKs is required for appropriate progression through the different stages of the cell cycle and entry into the next stage of the cell cycle. CDK4 and CDK6 are required for progression through the growth (G1) phase, CDK2 in the DNA synthesis (S phase) and CDK1 for mitosis and cell division (M phase). Regulation of the activity of the cell cycle CDKs is pivotal for correct timing of progression of the cell through the stages of the cell cycle and their activities are regulated at many levels, including complex formation with specific cyclins (A, B, D and E class cyclins; these cyclins are synthesized and degraded through the stages of the cell cycle), CDK inhibitors (CDKI), in particular CIP/KIP and INK-type CDKIs (see, e.g., Sherr et al., 1995), as well as phosphorylation and dephosphorylation at specific residues. The phosphorylation status of a specific threonine residue in the activation loop, the so-called T-loop, is a key modification for the activity of cell cycle CDKs (see, e.g., Fisher et al., 1994).
De-regulation of CDK activity is an important component of many disease states, generally through elevated and/or inappropriate activation, as CDKs themselves are infrequently mutated. Rare examples of mutations in cell cycle CDKs include CDK4 families with hereditary melanoma that result in insensitivity to the INK4 CDKIs (see, e.g., Zuo et al, 1996). Inactivating mutations in the CDKN2A gene, which encodes for p16INK4 and p14ARF CDKIs, are more common in hereditary melanoma (see, e.g., Hansson, 2010), these mutations also being associated with greater incidence of breast and pancreatic cancer in affected families (see, e.g., Borg et al., 2000). CDK4 and CDK6 can be amplified and/or overexpressed in cancer, their cyclin effectors, D-type cyclins, are also often amplified and/or over-expressed, whilst the CDK4/CDK6 inhibitors (INK4 genes) are frequently deleted in many cancer types and/or undergo epigenetic silencing (see, e.g., Ortega et al., 2002). E-type cyclins interact with CDK2 for its activity and are frequently over-expressed in cancer, whilst the p21 and p27 inhibitory proteins that act on CDK2, as well as CDK1, are epigenetically silenced in cancer (see, e.g., Malumbres et al., 2001; Jones et al., 2007). Up-regulation of the activities of cell cycle CDKs is therefore integral to cancer development and progression.
CDK7, another member of the CDK family, which complexes with cyclin H and MAT1, phosphorylates the cell cycle CDKs in the activation of T-loop, to promote their activities (see, e.g., Fisher et al., 1994). As such, it has been proposed that inhibiting CDK7 would provide a potent means of inhibiting cell cycle progression, which may be especially relevant given that there is compelling evidence from gene knockout studies in mice for lack of an absolute requirement for CDK2, CDK4 and CDK6 for the cell cycle, at least in most cell types (see, e.g., Malumbres et al., 2009), whilst different tumors appear to require some, but be independent of other interphase CDKs (CDK2, CDK4, CDK6). Recent genetic and biochemical studies have confirmed the importance of CDK7 for cell cycle progression (see, e.g., Larochelle et al., 2007; Ganuza et al., 2012).
In addition to its role as the CDK Activating Kinase (CAK), CDK7/cyclin H/MAT1, in complex with the basal transcription factor TFIIH, phosphorylates RNA polymerase II (PoIII) in its C-terminal domain (CTD) (see, e.g., Lu et al., 1995; Serizawa et al., 1995). CDK9, another member of the family, is also required for PoIII CTD phosphorylation. The PoIII CTD is comprised of a seven amino acid repeat having the sequence Tyrosine-Serine-Proline-Threonine-Serine-Proline-Serine (YSPTSPS), 52 YSPTSPS heptad repeats being present in the mammalian PoIII CTD. Phosphorylation of serine-2 (S2) and serine-5 (S5) by CDK7 and CDK9 is required for release of PoIII from the gene promoter at initiation of transcription. CDK7 appears to act upstream of CDK9, phosphorylation of S5 phosphorylation by CDK7 preceding S2 phosphorylation by CDK9 (see, e.g., Larochelle et al., 2012). Transcriptional inhibitors such as flavopiridol, as well as CDK inhibitors that inhibit CDK7 and CDK9 demonstrate the potential utility of CDK7 and CDK9 inhibition in cancer (see, e.g., Wang et al., 2008). In addition to their action in phosphorylating the PoIII CTD, CDK7 and CDK9 have been implicated in regulating the activities of a number of transcription factors, including the breast cancer associated estrogen receptor (ER) (see, e.g., Chen et al., 2000), retinoid receptors (see, e.g., Rochette-Egly et al., 1997; Bastien et al., 2000), the androgen receptor (see, e.g., Chymkowitch et al., 2011; Gordon et al., 2010), as well as the tumor suppressor p53 (Lu et al., 1997; Ko et al., 1997; Radhakrishnan et al., 2006; Claudio et al., 2006). CDK8, a component of the mediator complex that regulates gene transcription, through a mechanism involving interaction between transcription factors and the PoIII basal transcription machinery, also phosphorylates transcription factors to regulate their activities (see, e.g., Alarcon et al., 2009). CDK8 also appears to be important for regulating transcription reinitiation. The importance of CDK8 in cancer is highlighted by the finding that the CDK8 gene is amplified in 40-60% of colorectal cancers, whilst its cyclin partner, cyclin c, is upregulated in many cancer types, whilst functional studies are supportive of an oncogenic role for CDK8 in cancer (see, e.g., Xu et al., 2011). A potential role for CDK11 in regulating mediator activity has been described, indicating a role for CDK11 in transcription regulation (see, e.g., Drogat et al., 2012), whilst their ability to phosphorylate S2 the PoIII CTD also implicates CDK12 and CDK13 in transcription; CDK12 is also implicated in maintenance of genome stability (see, e.g., Bartkowiak et al., 2010; Blazek et al., 2011; Cheng et al., 2012).
In addition to the great deal of evidence implicating the above and other CDKs (e.g., CDK10; see, e.g., Lorns et al., 2008; Yu et al., 2012) in cancer, CDKs are also important in viral infections including HIV (see, e.g., Knockeart et al., 2002), neurodegenerative disorders including Alzheimer's and Parkinson's disease (of particular note here is CDK5, see, e.g., Monaco et al., 2005; Faterna et al., 2008), ischaemia, and proliferative disorders, including renal diseases (see, e.g., Marshall et al., 2006) and cardiovascular disorders including atherosclerosis.
The development of small molecule CDK inhibitors provides a potentially powerful approach in the treatment of many human diseases, in particular cancer. Thus inhibition of cell cycle progression may be achieved through the development of selective CDK1 inhibitors (as CDK1 appears to be indispensable for the cell cycle) or selective CDK7 inhibitors (as CDK7 regulates the cell cycle CDKs) or with inhibitors with activity against all of the cell cycle CDKs. Some evidence indicates that selective CDK4/CDK6 or CDK2 inhibitors may have utility for specific conditions (e.g., CDK4/CDK6 in haematological malignancies and CDK2 in glioblastomas or osteosarcomas), and so development of selective inhibitors for these CDKs may be of utility, the selectivity perhaps aiding toxicity issues.
Known Compounds
It appears that the following compounds are known.
CASRegistry No.Structure771502-87-5  771501-59-8  771509-61-6 771502-45-5  771508-20-4  1092443-65-6 1092443-63-4 1092444-59-1 1092444-58-0 1092444-23-9 1092444-03-5 1256288-39-7